This application is related to Japanese Patent Application No. 2000-120373 filed on Apr. 21, 2000, whose priority is claimed under 35 USC xc2xa7 119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a particle signal processing apparatus and a particle measurement apparatus using the same, such apparatuses being used for measurement of particles in body fluid and industrial particles.
2. Description of the Related Art
Conventionally, particle measurement apparatuses of the electric measurement type are provided with two chambers that communicate with each other through a micro through hole (orifice) and it is so arranged that when a particle-contained solution flows from one chamber to the other, a pulse-formed electric resistance change is detected as a particle signal each time a particle passes through the orifice. Since it is known that a peak value of the particle signal is proportional to a volume of the particle, the particle signal is utilized in calculating a particle diameter or in sorting out particles.
But problems with such particle signal measurement. apparatuses are that if bubbles contained in the particle-contained solution are present near the micro through hole, the obtained particle signal (pulse signal) fluctuates with respect to a base line (low frequency fluctuation) and it is difficult to determine the peak value of the particle signal accurately.
In view of the prior art described above, it is an object of the present invention to provide a particle measurement apparatus in which a base line of a particle signal including serial pulses is stabilized to determine a peak value of each pulse signal accurately and which permits measurement of particles with precision.
The object of the present invention is achieved by providing a particle signal processing apparatus which processes a particle signal representative of characteristics of particles, comprising: an amplifier having input and output terminals for amplifying a particle signal including serial pulses to output an output signal including the amplified serial pulses; a filter section for extracting a low frequency component from the output signal of the amplifier so that the extracted component is fed back into the input terminal as a negative feedback signal; a feedback signal control section for allowing the filter section to fix the negative feedback signal when each of the amplified pulses rises and to hold the fixed negative feedback signal while the amplified pulse is larger than a threshold value.